I am finishing some guitars I've been building out of African mahogany and crotch Walnut. To accentuate the grain and iridescence of the two woods, I was using an oil-based varnish (Danish or Tru-Oil), then a shellac sealer (Seal Coat by Zinsser) followed by a water-based grain filler (Target HSF) and HVLP-sprayed polyurethane topcoat (Target Oxford SuperClear). Although it looks marvelous, it takes an extraordinary amount of time, especially during the humid summer, and is hard to repair if I make a mistake. Can anyone recommend a quicker method that's generally water-based (low VOC) and accentuates the figure of these woods?
From contributor A:
Try using water base dyes. Clarity and iridescence are easily achieved with unlimited choices in color, tone etc. You can learn to pop the grain by experimenting. Use them for stain and/or toners and tints. They are quick drying and do not cause explosions or fires. I recommend Lockwood.
For the oil, I use a varnish. It dries a lot faster than oils or Danish oils.
For the WB filler and finishes, keep a fan blowing in the drying area to help it dry faster. Air movement helps a lot when the humidity is up.
I use Target Oxford Ultima Spray Lacquer (USL) with good results on rubbed-out mahogany, but previously I have used Crystalac 2000 with good results on guitars. These two brands help avoid the bluish cast that some of the earlier water based coatings gave.
You can put water soluble dye powder with some reducer right into the water based topcoat and apply it with an airbrush for sunburst shading on the guitar top. Use plenty of nearly dry-mist coats on top (or another shellac sealer coat) to avoid the color bleeding or lifting into the topcoats. I never tried the technical thing with a wet-film thickness gauge, but I am afraid to use less than four or five topcoats of wb. You don't have to wet sand between every coat, just when you start to see nibs or sags or a hint of orange peel. For me, that's at least every third coat.
Wait the manufacturer's recommended dry time before buffing, wet sand through about 1200 and then have at it with a lambswool buff on a 6" grinder/sander at low speed and some automotive buffing compound. Meguiars is nice, but you must recognize that there is a risk of silicone contamination for subsequent repairs or refinishing. With a guitar you have the option of using a large muslin buff on a drill press at slow speed and some white buffing compound. I settled on jeweler's white rouge – it is a little faster than the red stuff but not as harsh as brown.
Incidentally, Stewart-MacDonald has some useful information on guitar finishing. There's even a video on how to do sunbursts and gold-tops. They carry Crystalac 2000 (or used to) but I have subsequently switched to Target/Oxford.
I have to say, though, that all the snob vintage restorers and custom luthiers use good old nitrocellulose lacquer. I haven't followed this advice myself, partly because I don't have a safe place to spray nitro, and I get very good results with wb products with the added benefit of soap-and-water cleanup for the equipment.